Inversion of Enantioselectivity in Allene Gas versus Allyl Acetate Reductive Aldehyde Allylation Guided by Metal-Centered Stereogenicity: An Experimental and Computational Study

The use of gaseous allene as an allyl pronucleophile in enantioselective aldehyde reductive coupling is described. Notably, using the same antipode of chiral ligand, (S)-tol-BINAP, an inversion of enantioselectivity is observed for allene versus allyl acetate pronucleophiles. Experimental and computational studies corroborate intervention of diastereomeric π-allyliridium-C,O-benzoate complexes, which arise via allene hydrometalation (from a pentacoordinate iridium hydride) versus allyl acetate ionization (from a square planar iridium species).